The present invention relates to an electric rotating machine which can be reduced in size by improving the thermal conductivity of an insulating material used therein.
A method of improving the thermal conductivity of a main insulator used in the stator windings of an electric rotating machine is described in, for example, an article entitled "An Improved Insulation System for the Newest Generation of Stator Windings of Rotating Machines", CIGTE, 1994 Session, August 28-September 3, 11, 101. In the described method, the overall thermal resistance of the stator windings is reduced by filling the main insulation with fine particles made of an insulation material having a high thermal conductivity, such as alumina. Further, a main insulator formed by adding high thermally conductive particles or a composite of the particles and glass fiber into mica bonding layers is disclosed in Japanese Patent Application Laid-open No.63-110929 and Japanese Patent No. 127364 (1987). Furthermore, an insulation formed by bonding a tape made of mica and glass fiber cloth is disclosed in Japanese Patent No. 411834.
Although the thermal conductivity of a main insulator used in the stator windings of an electric rotating machine has been increased as described above, the overall thermal resistance of the main insulator of the stator windings can not be decreased when the heat load is increased as the electric power generating capacity increases. When the electric power generating capacity is increased, the voltage generated in the stator windings is generally increased and, consequently, the thickness of the main insulator must be increased in order to obtain a required electric insulating property. Particularly, in a case where the breakdown voltage per unit of thickness of the main insulator is low, the thickness of the main insulator increases. Therefore, when an attempt is made to increase the electric power generating capacity while keeping the size constant, the thickness of the main insulator has to be increased, and, accordingly, the machine size inevitably increases.